Electric discharge tube



'A. BOUWERS ET AL 2,093,002

anaemic DISCHARGE TUBE Filed Oct. 22, 1955 Sept 14, 1937.

Patented Se t. 14, 1937 UNITED STATES ELECTRIC DISCHARGE TUBE Albert Bouwers and Jac 'l-uuk, Eindhoven, -Ne N. V. Philips Gl hoven, Netherlands Application October 22,

ob Harmannus van der therlands, assignors to oeilampeni'abrieken, Eind- 1935, Serial No. 46,205

Germany November 14, 1934 9 Claims. (Cl. 250-35).

ention relates to electric discharge tubes and more particularly to discharge tubes capable of operating on very high voltages. Our invention is particularly well adapted to be used with X-ray tubes for very high voltages e. 3. 500,000 volts and more and will be explained in this connection; however it is not limited thereto, but may be used with discharge tubes of other types, such as tubes designed for the emission of corpuscular rays, for instance cathode rays.

Electric dischar have been constr The present luv ge tubes for very high voltages ucted with a tubular intermediate electrode placed between the cathode and the anode, which electrode divides into two stages the path in which the electrons are accelerated by the electric field. To further divide the discharge path, a plurality of such intermediate electrodes may be used.

In such discharge devices, the insulating portions of the tube wall are connected by means of metal rings which are mechanically secured and electrically connected to the respective intermediate electrodes: Such a construction had the disadvantage that the tube became quite long, and furthermore, there was the possibilitythat flash-overs might occur over the surface of the insulating portions of the tube wall.

The purpose of our invention is to reduce the overall length of such tubes and to decrease the possibility of flash-overs occurring.

In accordance with our invention a considerable reduction in the overall length of such tubes and a greater protection against flash-overs are obtained by providing the insulating portions of the tube wall with re-entrant parts which are sealed to the intermediate electrode and surround same with an intermediate space. These re-entrant parts take up a portion of the potential to be absorbed by the insulating wall portion.

In order that the invention may be clearly understood and readily carried into effect, it will now be more fully described with reference to the accompanying drawing, in which;

Figurel is a side'elevation of an X- according to a prior construction;

Fig. 2 is a diagrammatic view in section of an X-ray tube according to the invention;

Fig. 3 is a sectional view of an X-ray tube according to another embodiment of the invention;

Fig. 4 is a cross-sectional view taken along the line IV-IV of Figure Fig. 5 shows on an enlarged scale a detail of the x-ray tube of Fig. 3;

ray tube I Thering 3 may consist of two me Fig. 6'is another modification of a tube made in accordance with .the invention.

The advantagesof tubes made in accordance with our invention can be moreeasily appreciated if compared with the known construction as shown for example in Fig. 1. This figure shows a known X-ray tube which comprises a bulbous glass vessel l containing a'cathode .5 and a seci 0nd bulbous glass vessel 2 containing an anode 6; these vessels being hermetically sealed with their neck portions to the end of a metal ring 3. tal rings, sealed and hermetically ends. Mechanat one end to the vessels l and 2 sealed together at their otherically'secured to and electrically connected to the ring 3 and extending into the vessels l and 2 is a tube 4 acting as an intermediate electrode. The tube 4 serves as a transmitting tube for the electrons emitted by the cathode 5, whereby the electrons pass through the tube 4 at a speed corresponding to the potential difference set up between the cathode 5 and the tube 4 and, upon emerging therefrom, are further accelerated by the potential applied between the tube 4 and the anode 6.

The X-ray tube shown in larly to the tube sho Fig. 2, consists simiwn in Fig. 1, of two bulbous glass containers 1 and 8, within which are arranged cathode 5 and anode '6 respectively. However, in accordance with the invention, the containers 1 and 8 are provided at their adjacent sides withre-entrant portions 9 and I0 respectively, which are hermetically sealed to the ends of an intermediate metal tubular electrode ll interconnecting the containers 1 and 8. The reentrant portions 9 and I0 surround the tubular electrode II with an intermediate space and therefore will'take up a material portion of the potential diflerence occurring over the glass walls of the containers 1 and 8, whereby the danger of arcing over is considerably reduced.-

Although a potential diiference exists between the adjacent mouth portions of the re-entrant portions (indicated by 40 and 4|), the distance that these portions must be spaced apart to avoid a breakdown therebetween can be made considerably less than the distance that would. be required to prevent a. creeping discharge over the surface of a'glass wall for the same potential difference.

Because of this, the intermediateelectrode l I can be made considerably shorter than the electrode 4 of Fig. 1, and as a result the distance between the centers ot containers I and I and thus 54 the overall length of the tube are much less than I those of the tube shown in Fig. 1.

Due to the decreased length of electrode II, a smaller number of electrons are drawn from the discharge between the cathode 5 and anode 8 and thus there is smaller loss of electrons. This is because, in passing through a long narrow tube, some of the electrons are taken up thereby, and the longer the tube the more electrons will be lost in this way as only a slight deviation from the axial direction causes an electron to impinge upon the wall of the tube rather than leave through the end thereof. Thus a decreased length of the tubular electrode II is advantageous in that there will be a smaller loss of electrons. That the invention brings about this advantage is obvious by comparing Figures 1 and 2.

To prevent a breakdown between the adjacent portions of the glass walls of containers 1 and 8in the vicinity of points 48 and 4|discs l2 and I3 of insulating material are provided between these portions. The insulating properties of these discs may be improved by giving them a saucer shape so that they extend substantially parallel to the spherical wall portions of the containers 1 and 8 respectively.

The X.-ray tube shown in Fig. 3 comprises a cathode portion A and an anode portion B. The cathode portion A has an envelope l4 consisting of a cylindrical metal ring i9, for instance of chrome iron, to the ends, of which are hermetically sealed vitreous portions 20 and 2.| having reentrant parts 39 and I1 respectively. To the re-entrant part 39 is hermetically sealed a cathode structure having an incandescible cathode provided with lead wires 35 and 35' for connection to a suitable voltage supply, not shown.

Similar to portion A, the anode portion B has an envelope l5 consisting of a central metal ring 22, for instance of chrome iron, sealed with its ends to vitreous portions 23 and 24 having re-entrant parts l8 and 42 respectively. To the end of re-entrant portion 42 is hermetically sealed an anode 26 provided with an axial cavity 43 having on its bottom surface a target 34, for instance of tungsten. The wall of the cavity 43 is provided with an aperture 44 through which the X-rays generated on target 34 pass to leave the tube through a window 21 hermetically sealed in the ring 22. The anode 26 is provided with a hollow tubular conductor 38 which serves to supply current to the anode, and also to convey a cooling fluid to the anode, cooling same during the operation of the X-ray tube.

Interconnecting portions A and B and hermetically sealed at its ends to the re-entrant parts I! and .I8 is an intermediate .electrode IS in the shape of a metal tube, for instance of copper.

The electrons emitted by the incandescible cathode 25 pass through tube l8 and impinge on target 34 to generate thereon X-rays which leave the X-ray tube inthe manner above described.

Insulatingly separating the two portions A and f B are two members 28 and 29 of insulating material, for instance the material known under the trademark Philite, provided with flanges 28' and 29' extending a considerable distance along the cylindrical portions of the vitreous members 2| and 23. The members 28 and 29 are of similar shape with the exception that member 29 is provided with a bore 30 filled with a suitable insulating mass such as paraffin through which passes a supply wire 3| connected to the tube It and serving to apply potential thereto, (see Fig.

4) and a second supply wire 38 the purpose of which will be explained hereinafter. The members 28 and 29 are securedtogether at their adjoining surfaces (indicated by 45 in Figure 4) by means of a suitable adhesive, whereby no gaps will exist between these surfaces. Due to the fact that the flanges 28' and 29' extend fora consider-.

are filled with a hardening insulating material,

for instance litharge.

Fig. 5 is a sectional view of the cathode construction. The supply wires and 35' are hermetically sealed in the stem and a metal cap 46 serving as a focussing device is sealed to the neck of the re-entrant portion 39. A plate 41 of a material opaque to X-rays, for example tungsten, is disposed in the cap 48 and prevents X-rays from escaping in an axial direction. The spirally wound filament 25 is mounted on a metal stem 48 secured to the plate 41. The outer end of the filament is connected to the supply wire 35' which is led through an aperture in the disc 41 but insulated therefrom by a glass bead 49. A disc 58 mounted on the wire 35' intercepts the X-rays escaping through the glass bead 49. The supply wire 35 terminates atthe metal plate 41 and is thus connected spirally wound filament 25.

At the side of the stem 45 is a small metal plate 5|, supported by a bent wire 53 mounted on the stem 45. Plate 5| is of circular shape, but appears elliptical as it is inclined at an angle of about 60 to the plane of the drawing. This metal plate has applied to it a getter substance. After the tube isduly evacuated the substance is vaporized by the application of heat. The vapour is precipitated on the surrounding walls and thereby absorbs undesired gases present in the tube which gases would otherwise give rise to harmful ionization and arcing over, especially because the tube is tobe used with very high voltages. The use of a getter for cleaning-up residual gases is of special importance for tubes of the kind described, tor the following reason.

The hollow tube I3 will best be made of two to the inner end of the sections shut off by a temporary window, for

example made of copper or glass. The two parts A and B are separately evacuated and sealed oil, whereafter they are positioned with respect to each other and the two sections of the tube l8 welded together. Finally the windows are removed, for example by melting them down or by mechanical means. This causes a considerable quantity of gas to be introduced into the evacuated space which could be injurious to the action of the tube under high tension. The cleaner mounted at the cathode side of the tube removes these gases from the discharge space. One or more apertures 52 are provided in the cap 48 for free communication between the spaces separated by the neck of the re-entrant portion 38 and the ther explanation. The getter substance may consist of barium enclosed in a thin copper jacket 54.

The device schematically shown in Fig. 6 serves for the genera tion of hard cathode rays. It consists of three portions A, B and C. The portions A and B are similar to the portions of the device shown in Fig. 3. -Anthird portion C is inserted in the connection between A and B. Either of the 10 three portions comprises an enclosing envelope consisting of a metal portion (53, 53', 53") symmetrically mounted between twoglass portions (54, 55, 54, 55', 54", 55"). The cathode portion A provided with a cathode 56 having supply wires 57 is connected to the middle portion C by a metal tube 59 conforming to the tube l5 of Fig. 3 and the latter portion is connected to the anode portion B by a similar metal tube 60. The anode 58 consists of a metal tube closed at the end by a thin window of a metal having a low atomic weight such as aluminium or beryllium. Through this window cathode rays emitted by the cathode and accelerated in three stages may pass into. the open air. The tubes 59 and 60 are surrounded by re-entrant glass portions GI, 62, 63, and 64. The distance a between adjacent glass parts of the wall is considerably shorter than the distance b between the points of connection of theseglass parts to the connecting metal tube, a material 80 reduction of the overall length of the discharge device being the result thereof. Insulating sleeves as those denoted by 28 and 29 and concentratin coils indicated by reference numeral 37 in Fig. 3 may be used as well in a multiple tube consisting of three or even more parts.

During the operation of the X-ray tube shown in Fig. 3, the voltage applied between the anode 26 and'the cathode 25 is divided between the four vitreous portions 20, 2|, 23, and 24. For this purpose the conductor 3! is connected to the middle of the supply, whereas if desired, the metal rings is and 22 may also be given a suitable potential.

For focusing the beam of electrons and thus 5 preventing leakage to the tube IS, a coil 31 is provided around the right-hand portion of tube It. One end of the coil is directly connected to the tube 16, the other end being connected to the lead 38. For energizing the coil 31, leads 3| and 50 38 may be connected to a suitable supply of direct current (not shown).

It will be noted that, due to the fact that the adjacent ends of the portions A and B are bent back toward the ends of,the tube "5, the overall 55 length of the X ray tube can be considerably reduced.

Discharge tubes constructed according to the invention, having an overall length of about 40 centimeters are suitable for operation with oper- 60 ating voltages of more than two hundred kilovolts.

If desired in connection with extraordinarily high. voltages a tube according to the invention may consist of more than two portions, the inter- 65 mediate portions having a hollow tube as the tubes ii and I6 and re-entrant portions surrounding them at each end. 4

While we have described our invention in connection with specific examples and in certain ap- 70 plications, we do not wish to be limited thereto,

but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What we claim is: 1. An electric discharge tube for high voltages 75 comprising, an anode portion and a cathode portion, saidanode portion comprising an envelope containing an anode and-having an -insul'ating portion provided with a re-entrant part opposing the anode, said cathode portion comprising an envelope containing a cathode and having an 5 insulating portion provided' with a re-entrant part opposing the cathode, a hollow intermediate electrode interconnecting said anode and cathode portions with itsv ends sealed to the ends of said re-entrant parts, said re-entrant parts surround- 10 ing said intermediate electrode and being spaced from each other so as to take up a portion of the potential difference occurring over said insulating portions.

2. An electric discharge tube for high voltages 15 comprising, an anode portion comprising an envelope containing an anode and having an insulating portion provided with a re-entrant part,

a cathode portion comprising an envelopecontaining a cathode and having an insulating por- 20 tion provided with a re-entrant part, a hollow intermediate electrode interconnecting said anode and cathode portions with its ends sealed to the ends of said re-entrant parts, said reentrant parts surrounding said intermediate 25 electrode and taking up part of the potential difference occurring over said insulating portions. and members of insulating material encircling said electrode and extending between the insulating portions of said envelopes to insulate same 30 from each other.

3. An electric discharge tube for very high voltages comprising, an anode portion comprising an envelope containing a cathode and having an insulating portion provided with a re-entrant part, a cathode portion comprising an envelope containing a cathode and having an insulating portion provided with a re-entrant part, a hollow intermediate electrode connecting said anode and cathode portions and sealed with 40 its ends to the ends of said re-entrant parts, said re-entrant parts surrounding said electrode and absorbing part of the. potential difierence occurring over the insulating portions of said envelopes, and insulating members encircling said electrode and extending between said anode and I cathode portions, said members having cupshaped extensions extending over the insulating portions of the envelopes. I

4. an electric discharge tube for very high voltages comprising, an anode portion compris-. ing an envelope containing an anode and having an insulating portion provided with a re-entrant part, a cathode p'ortion comprising an envelope containing a cathode and having an insulating portion provided with a re-entrant part, a hollow intermediate electrode interconnecting said anode and cathode portions with its ends sealed to the ends of saidre-entrant. parts, said re-entrant partssurrounding said electrode with-intermediate spaces and taking up part of the potential difference occurring over said insulating portions, members of insulating material encircling said, electrode and extending between said insulating portions, and an insulating material within the spaces formed between said re-entrant parts and said electrode.

5. An electric discharge tube for very high voltages comprising, an anode portion comprising an envelope containing an anode and having an insulating portion provided with a re-entrant part, a cathode portion comprising an envelope containing a cathode and having an insulating portion provided with a re-entrant part. a hollow intermediate electrode connecting said anode .76

4 and cathode portions with its ends sealed to the ends of said re-entrant parts, said re-entrant parts surrounding said electrode with intermediate spaces and being spaced from each other so 5 as to take up part of the potential diflerence occurring over said insulating parts, and an electric coil within one'oi said spaces and surrounding said hollow electrode to assist in projecting the discharge through, the hollow portion of said in electrode.

8. An electric discharge device comprising a cathode and an anode and at least one hollow tubular member mounted between said cathode and anode and serving as an intermediate electrode, 15 enclosing envelopes carrying said anode, cathode and member, each 0! said envelopes having a reentrant part of insulating material surrounding said member, adjacent re-entrant parts being spaced from each other and being secured to said 20 member, the distance between the points at which said re-entrant parts are secured to said member being considerably greater than the smallest distance between said parts. A 7. An' electric discharge tube for very high 25 voltages comprising a plurality of envelopes having insulating'portions. provided with re-entrant parts, an anode within one oi! said envelopes, a cathode within another of said envelopes, and a hollow intermediate electrode between said anode and cathode, said electrode having one end secured to the end 0! one of said re-entrant parts and having its other end secured to the end of the re-entrant part of.the adjoining envelope and being surrounded by said re-entrant parts, said 35 re entrant parts being spaced from each otherso as to absorb a portion of the potential diflerence occurring over said insulating portions.

8. A high-vacuum electric discharge tube comprising, a closed envelope having a plurality of cathode within one of said envelope portions, an

anode within another 0! saidenvelope portions, and a getter substance within one 01 said envelope portions.

9. A high-vacuum high-voltage electric disa charge tube comprising a plurality of envelopes each having re-entrant parts of insulating material, an anode within one oi! said envelopes, a cathode structure within another or said enve lopes, and a hollow intermediate electrode be tween said anode and cathode structure and connected at one point to one of said re-entrant parts and at another point to a .re-entrant part of the adjacent envelope, said two re-entrant parts surrounding said electrode and being spaced apart, the distance between said points of connection being considerably greater than the distance between said parts, said cathode structure comprising a hollow metal cap member provided with an aperture, a glass stem supporting said cap and forming part of the savelope portion enclosing the cathode structure, and a filament mounted within said cap, and a getter material mounted in the space formed by said cap and stem and in restrictive communication with the discharge space of the tube.

ALBERT BOUWERS.

JACOB HARMANNUS VAN nan TUUK. 

